This question is based on greatest common factor.
There are 45 red buttons and 60 yellow buttons
factors of 45 = 3,5,15
factors of 60 = 2,3,4,5,6,12,15
Hence the highest common factor is 15
Narci can use 15 boxes to divide buttons equally.
She can divide 45 red buttons in 15 boxes by putting 3 buttons in each box.
She can divide 60 yellow buttons in 15 boxes by putting 4 buttons in each box.